1. Field of the Invention
This invention relates to an endoscope with which a front field of view and a lateral field of view can be observed simultaneously.
2. Description of the Related Art
Endoscopes have been widely used in medical fields and industrial fields in recent years. An endoscope can observe an inside of a subject by inserting an elongated insertion portion into the subject. Various types of such endoscopes have been proposed and put into practical use including, for example, a front-view type endoscope in which an observation lens or an illumination lens is provided in a distal end face of a distal end portion that is provided on a distal end side of an insertion portion, and a side-view type endoscope in which an observation lens or an illumination lens is provided at a part of a side face of a distal end portion of an insertion portion.
Furthermore, recently, in order to widen the observation range, various endoscopes that are configured to enable observation not only in a field of view in front of a distal end portion of an insertion portion, but also in a field of view in a circumferential direction that is laterally located along the circumference of the outer circumferential side face of the distal end portion at the same time have been proposed in, for example, Japanese Patent Application Laid-Open Publication No. 2011-152202 and Japanese Patent Application Laid-Open Publication No. 2008-228810, and put into practical use.
Such kinds of endoscopes have a configuration that includes front illumination means for illuminating a front field of view range, and lateral illumination means for illuminating an entire lateral circumference field-of-view range. As the aforementioned lateral illumination means, for example, a device has been proposed which illuminates the entire lateral circumference by scattering an illuminating light that has been optically guided from a light source to a distal end side in the longitudinal direction of an insertion portion of the endoscope using a light guide fiber or the like in the radial direction of the insertion portion.
Further, some conventional endoscopes include means for measuring the amount of reflected light from an observation target and detecting a luminance distribution of the observation target. In an endoscope disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2011-019692, luminance distribution information that is detected in this manner is used for calculating a photographing distance between the distal end portion of the insertion portion and the observation target.